In a known process for recovering metals, particularly light metals, waste metal is ground in beater mills to form a fine-grained fraction, which is treated in a small-nip roll mill and is subsequently sieved or subjected to air separation. The rolls of the roll mill rotate preferably at different circumferential velocities (German Patent Publication No. 28 53 256).
It is also known to treat slags which have become available in metallurgical operations and contain watersoluble constituents. Here the slag is disintegrated to form a particulate bulk material, which is then washed to remove salt, and the resulting salt-containing slurry is treated in a decanting basin, from which a salt solution is withdrawn, and subjected to evaporation (Open German Application No. 27 46 860).
In the processes known in the art the aluminum-containing fused slag is first crushed and then ground. The subsequent sieving or air separation provides a fine fraction, which is smaller than 8.0 mm in diameter. In that practice, metallic aluminum in a purity above 90% can be recovered only up to 35% of its content in the salt-containing slag. A crushing to a smaller size will not be possible unless a high degree of wear of the crushing elements under the action of the corundum, spinel and quartz contents of the aluminum-containing fused slag can be tolerated.
Another disadvantage of these known processes resides in that the leaching of the relatively large particles takes a relatively long time. As the leaching operation is intermittent, gases will also be intermittently evolved during that operation and for this reason can be rendered innocuous only with difficulty.